"start" > "run" > "cmd" to open the command prompt window. Type "NETSTAT -a -n" at the command prompt, and then press Enter to digitally view the port number and status of TCP and UDP connections.
Command format: Netstat? -a-a -n -o -s?
-a displays all active TCP connections and TCP and UDP ports that the computer listens to.
-e indicates the number of bytes and packets sent and received by Ethernet.
-n indicates that only the addresses and port numbers of all active TCP connections are displayed in digital form.
-o displays the active TCP connections, including the process ID(PID) of each connection.
-s indicates that statistics of various connections, including port numbers, are displayed by protocol.
Close the port
For example, to close port 25 of SMTP service in Windows 2000/XP, you can do this: first open the control panel, double-click the administrative tools, and then double-click the service. Then find and double-click the Simple Mail Transfer Protocol (SMTP) service in the opened service window, click the Stop button to stop the service, then select Disable in the Startup Type, and finally click the OK button. In this way, closing the SMTP service is equivalent to closing the corresponding port.
port
If you want to open the port, just select Automatic in the startup type, click OK, then open the service, click Start Enable Port in the service status, and finally click OK.
In addition, in the network connection properties, select the "TCP/IP Protocol" property to open advanced TCP/IP settings, and open TCP/IP filtering in the options page. In the setting window that appears, you can also set the opening and closing of the port according to the implementation. By default, TCP/IP filtering is not enabled.